Electrodynamic ultrasonic transducers are used predominantly in the field of the non-destructive testing of workpieces.
Such electrodynamic ultrasonic transducers consist of magnet systems which introduce magnetic lines of flux into the workpiece to be tested. A coil system arranged in the vicinity of the surface of the workpiece is acted on by high frequency alternating current so as to inductively produce eddy currents in the surface of the workpiece. The electrons of the workpiece which are moved in this manner interact with the magnetic field introduced. As a result, a coupling to the crystal lattice of the workpiece is produced, and sound is produced which can be used for testing the workpiece. Such an electrodynamic ultrasonic transducer of the type indicated above is known from an unexamined German Patent Application 32 34 424. The electrodynamic ultrasonic transducer consists, in that case, of a magnet arrangement in which magnets having the same polarity are arranged facing each other over ferrite parts lying between them.
In this known embodiment, the surface area of the ferrite parts adjacent and parallel to the pole surfaces of the magnets are at least as large as the cross-sectional area of the pole surface themselves. It must, however, be noted in connection with this known arrangement that while magnetic lines of flux are concentrated on the region of the ferrite part, they only in part, form a magnetic return through the workpiece to be tested. In other words, magnetic lines of flux also emerge laterally, i.e., not directly towards the surface of the workpiece, and, thus establish a magnetic return via the air. The disadvantage is therefore that, in this case, only a part of the entire available magnetic field is used for ultrasonic testing.